Store hashbang comments with unique comment type

Summary:
Currently, the Hermes parser stores hashbang comments (comments that begin with `#!` and start at the first byte of the file) as regular line comments. Let's introduce a new `Hashbang` comment type for these comments as they are not actually regular line comments, and so that they can be easily distinguished.

This will be used to distinguish these hashbang comments from other line comments in the Hermes parser compiled to WASM.

Reviewed By: avp

Differential Revision: D24352504

fbshipit-source-id: 653a8c2efd7bd188ee89a64c465905ad2ccdd6ca

include/hermes/Parser/JSLexer.h

@@ -268,6 +268,8 @@ class StoredComment {
     Line,
     /// Comment that is delimited by "/*" and "*/".
     Block,
+    /// Comment that begins with "#!" and starts at the first byte of the file
+    Hashbang,
   };
 
   StoredComment(Kind kind, SMRange range) : kind_(kind), range_(range) {}
@@ -276,14 +278,14 @@ class StoredComment {
     return kind_;
   }
 
-  /// \return the comment with delimiters (//, /*, */) stripped,
+  /// \return the comment with delimiters (//, /*, */, #!) stripped,
   /// as a StringRef which points into the source buffer.
   StringRef getString() const {
     // Ignore opening delimiter.
     const char *start = range_.Start.getPointer() + 2;
     // Conditionally ignore closing delimiter.
-    const char *end = kind_ == Kind::Line ? range_.End.getPointer()
-                                          : range_.End.getPointer() - 2;
+    const char *end = kind_ == Kind::Block ? range_.End.getPointer() - 2
+                                           : range_.End.getPointer();
     assert(end >= start && "invalid comment range");
     return StringRef{start, (size_t)(end - start)};
   }

lib/Parser/JSLexer.cpp

@@ -1117,7 +1117,9 @@ const char *JSLexer::skipLineComment(const char *start) {
 
   if (storeComments_) {
     commentStorage_.emplace_back(
-        StoredComment::Kind::Line, SMRange{lineCommentStart, lineCommentEnd});
+        start[0] == '/' ? StoredComment::Kind::Line
+                        : StoredComment::Kind::Hashbang,
+        SMRange{lineCommentStart, lineCommentEnd});
   }
 
   return cur;

unittests/Parser/JSLexerTest.cpp

@@ -1083,6 +1083,18 @@ TEST(JSLexerTest, StoreCommentsTest) {
     EXPECT_EQ("world", lex.getStoredComments()[1].getString());
   }
 
+  {
+    JSLexer lex("#! hello world\n;", sm, alloc, nullptr, true, false);
+    lex.setStoreComments(true);
+
+    ASSERT_EQ(TokenKind::semi, lex.advance()->getKind());
+
+    ASSERT_EQ(1, lex.getStoredComments().size());
+    EXPECT_EQ(
+        StoredComment::Kind::Hashbang, lex.getStoredComments()[0].getKind());
+    EXPECT_EQ(" hello world", lex.getStoredComments()[0].getString());
+  }
+
   {
     JSLexer lex("/**/;//\n", sm, alloc, nullptr, true, false);
     lex.setStoreComments(true);